Siemens AFCI plug in circuit breakers are intended for use in Siemens EQ, Siemens Ultimate, ITE, and Gould load centers or meter combinations. The double pole Siemens breakers may be used in single or 3-phase load centers and are 240V rated. To ensure the warranty on a Siemens panel is not voided, the use of Siemens breakers is required. The combination type AFCI is for use in areas enforcing the 2008 or newer National Electric Code. Check with your local electrical inspector to confirm. The use of a double pole AFCI allows for shared neutral applications in which two circuits will share a common neutral. This device is in a clamshell package. Siemens strongly recommends against the use of "used" breakers. The installation of used breakers in a Siemens panel will void the warranty on the panel. Siemens does not sell used breakers and has not approved any 3rd party sellers to do so.